This invention relates to a targeting device for x-ray locating during the extracorporeal treatment of patients with focused shock waves, particularly for a lithotritor.
Non-invasive lithotrity with focussed shock waves requires the precise locating of the stone and a precise positioning of the patient with respect to the focal point in which the shock waves meet.
So far, x-ray locating and the locating of ultrasonic devices have been used (German Patent Document DE-PS 34 26 398). While the ultrasonic locating can be carried out continuously, a permanent "x-ray filming" is eliminated because of the radiation stress. On the other hand, not all types of stones can be sufficiently imaged by the ultrasonic device.
From the German Patent Document DE-PS 39 19 083, corresponding to U.S. Pat. No. 5,070,861 to Einars et al., a targeting device for x-ray locating is known in the case of an extracorporeal treatment of patients with focussed shock waves, particularly for a lithotritor, which has a carrier which is made of an x-ray negative material, can be fastened to the shock wave source and carries at least four x-ray positive reference points of which at least two are situated on a first straight line which leads through the focal point of the shock waves and of which at least two others are situated on a second straight line which also leads through the focal point of the shock waves.
When this targeting device is used according to the "notch-and-bead principle", the x-ray C-arc must be brought into two specific discrete positions. A targeting device would be desirable which indicates the focal point in any arbitrary position of the x-ray C-arc.
It is therefore an object of the invention to provide another targeting device by means of which the focal point of the therapy unit is also visible without any rough adjusting of the x-ray C-arc.
This object is achieved by a targeting device wherein the x-ray positive elements are straight-lined and are arranged on straight lines which intersect in the focal point of the shock wave system.
By means of the targeting device according to the invention, a positioning can take place by means of an x-ray C-arc which comprises an x-ray tube and an image enhancer opposite the x-ray tube, with a few images and irrespective of the position of the x-ray C-arc since the focal point can be recognized on every x-ray image.
As the "vanishing point" of the straight elements, the focal point is easily recognizable on every x-ray image which reduces the number of images to be taken. In preferred embodiments, three or four elements are used. This number is sufficient for obtaining clear results.
An x-ray negative material, such as the synthetic material Delrin, is considered for the carrier. If possible, the carrier should not be visible on the projecting screen. The mass distribution perpendicularly to the irradiation direction should be as homogenous as possible. The outer contour should be body-friendly on the side facing the patient; that is, it should have no sharp edges. It should be as simple as possible to fasten the carrier to the shock wave source and to remove it again, and the carrier should be so sturdy that the targeting direction under a load of approximately 30 kg deforms only to such an extent that a displacement of the straight target line remains in the millimeter range. Such a load may occur when the targeting apparatus bumps against the patient's body.
The reference elements should be made of a material that is as x-ray positive as possible and is rich in contrasts on the projecting screen. Suitable materials are all metals, particularly those with a high atomic number, such as steel, lead or soldering tin with a high lead content.
The carrier may have the shape of a hollow body, such as a cylinder. The x-ray positive elements will then, for example, be tensioned steel wires. Other shapes are also possible, such as the shape of a truncated cone or that of a cone, on the corresponding shell surfaces of which the metallic x-ray positive elements are arranged. All carriers have in common that the x-ray positive elements all extend toward a point outside the carrier which is the focal point of the shock wave source.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.